Again, I'd try a couple cans of diesel purge. You've got a pump that sat for a good while without being run with who know's what inside. You could have all kinds of build up and varnish that is keeping everything from working properly. The diesel purge will clean out anything inside. If it doesn't help you've only put a few bucks into it.

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If you try a solvent like diesel purge do not just run it through the injection pump. Shut the engine down and let it soak awhile.

Some have even used gasoline as a solvent. That is very slow acting on varnish type deposits unfortunatly. That and laquer thinner of course you do not run the engine on. Laquer thinner is death on varnish type buildups.

My understanding of your symptoms is that you have an engine that smokes blue smoke, (At Idle only, Only under load, Only at a cretin speed?), will not idle on its own until warm, and returns to idle slowly.

If my understanding is correct, then I will toss my hat in the ring for two of the three issues, however keep in mind that free advice is worth every penny.

(Provided that the linkage is eliminated as a source of any binding which prevents the throttle lever from contacting the vertical throttle stop screw without delay);

The unwillingness to idle when cold, and slow return to idle, point to the Idle Governor setting. From what you described, I would say that the Idle Governor spring tension needs to be increased. If it is too low, or soft, the Idle Governor spring can not force the counter weights back to increasing fuel at idle when cold, or regulate the idle speed as loads are introduced and taken away.

Since the Idle Governor is not strong enough to handle controlling the idle speed, the governed idle speed would be too low, and as a result the traditionally understood way to increase the idle speed is to adjust the vertical throttle stop, which increases the idle speed, but, since the throttle is now handling the idle speed, the idle Governor can't regulate the idle as it would if it were controlling the idle.

The slow return to Idle is happening because; the throttle spring does not let the rack return back "past" the idle setting for a moment, before settling in the regulated idle position. This return is noticeable when the engine is cold, at about 2500rpm, and you suddenly take your foot off the throttle. The engine will seem to die and then ketch at the idle speed. That is the Idle Governor working.

The Idle Governor spring tension adjustment is inside the IP, and is very easy to mess up. If you have a good Pump shop in your area, you might convince one of the old guys there that will know what you are talking about to make the “adjustments” on the car for you. It is amazing what a difference a turn here and a turn there can do, as long as the person turning knows what they are doing.

It would be a shame to have to open the can of worms that replacing the IP could when all that is needed is an adjustment.

Injection Timing Device on Your engine will have NO Bearing whatsoever as to the Quantity Of Fuel Injected.
--Only WHEN its injected.....

BOSCH SEEMS TO SAY LEAKY SEALS AT RACK CAN CAUSE THE "FLOATING IDLE"... I know nothing about the innside of the injection pump, my service manual shows nothing.....

(I'm guessing your bosch tech was thinking EP-VE type pump, and NOT PES 5MW/M when he gave you his diagnosis, as the EP-VE Rotary does have an Internal Timing-Device, that can and does stick--Your Pump has no such device--Its In The Engine)

This guy is MB trained, 20 yrs hands on under the hood...

Your Timing Device is part of the chain Sprocket that Drives the pump--a collection of weights and springs--very reliable part....

BOSCH SAYS FAULTY TIMING DEVICE CAN ADVANCE TIMING ABNORMALLY CAUSING THE SUSTAINED RPM PROBLEM

If the Rack is in Idle position then it WILL idle. There are no seals that can wear that would cause your symptoms on the PES 5MW/M pump.

Can you by chance supply details about the interior of the IP??

--Something is Causing the Rack to Stick....Prolly iffy stop-diaphragm or summit in the Governor--IF its an Injection pump fault, which I suspect not.....

NO WAY I CAN COMMENT.....

OR you are getting Oil into the engine (Turbo maybe??) which is adding to the fuelling and keeping it running higher than idle....

INTAKE PIPE INTERIOR AT BOOST AIR FEED IS DRY, NO OIL...

One thing to check/replace would be the Lift-Pump. This Can in certain cases, leak engine oil Into the fuel--which could be giving your symptoms....[/QUOTE]

THAT SOUNDS LIKE A LONGSHOT.....

ALISTAIRE, ARE YOU A IP BOSCH TRAINED PUMP GUY, SOUNDS LIKE IT...

Agh CAPS!

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Alistaire you are pretty brazen man, blithely over ruling the representative from the manufacturer bosch without providing a shred of reasoning why you would posses such authority, such as for example "I was trained by Bosch", or "Ive been rebuilding those units for years" , or "I'm a MB tech" ....

Can you back up what you say with anything more than sweeping statements directly contradicting a trained MB tech with a few decades of under the hood hands on who is making sense?

The timing advance mechanisim on our type of in line pumps is not a part of the pump. It is located between the injection pump and the chain drive. A centrifical advance mechanical device. Even if defective when the rack shuts down to idle the engine would also come down in revs as no fuel is available to allow higher when normal.

The mechanical timing wheel or advance mechanisim would just make the engine knock probably or stall out if still totally advanced at idle. The main thing here is that that device has nothing to do with the problem you describe.

This is just common sense anyways. If you are pressed to find fault it is your expert advisor. As suggested he has his pumps mixed up perhaps as the logical answer.

Certainly I can be wrong or anyone else. I at this point would want to know if the last person running your pump on an engine had the problem. Or it is a new problem. If new a good soaking has a chance.

The gentleman that mentioned a direct feed of a secondary fuel supply delaying the slow down has some merit as well. It is not impossible but somewhat strange. I would not rate the chances of it too highly. That still does not mean it is impossible.

Certainly am 'Brazen' when I see something that is Blatently WRONG!
--Cant help that--the way I am. Can't stand B.S.
You asked for help and opinions on the fault, they have been given by replies.

Its entirely up to You who you believe, But I'll say this-

An M.B. Technician will not be rebuilding the INJECTION-PUMP. He has neither the knowledge or equipment in Most cases.

This work is nearly Always farmed out to those Co's that have the Required Specialist Injection Technicians And Equipment such as a Proper Pump Test-Bench and ISO Test-Plans to service and set them up. Not even a Main Stealer has such equipment.

Yes, Ive been on Bosch Training Courses for both the Inline (PES) and Rotary (EP-VE) pumps and their associated 'modules' I am pretty familiar with the operation and repair of such devices.

I am firmly the opinion that your tech was thinking of the Rotary Bosch pump when he made his erronious diagnosis, as his diagnosis was more inline with a Rotary EP-VE pump fault...

(I'm guessing from your above reply this diagnosis was made by an M.B. tech and not a Specialist I.P. Tech)

-=-=But Hey--Thats MY opinion!--There's NO reason for you to be so 'Brazen' and Abrasive in your reply Yourself, when all I was trying to do was help ya!!

(Wont bother in future....)

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Alastair AKA H.C.II South Wales, U.K. based member

W123, 1985 300TD Wagon, 256K,
-Most recent M.B. purchase, Cost-a-plenty, Gulps BioDiesel extravagantly, and I love it like an old dog.

W114, 1975 280E Custard Yellow,
-Great above decks needs chassis welding--Really will do it this year....

I think I will follow your suggestion. I have a spare ip from the 380K miles motor I took out .... it seemed to be working ok ...

Now that I have it sitting on the bench I can see how easy it would be to place it on its side, pour lacquer thinner into the hole where the lift pump fits or the oil fill hole on the "sticky" pump after installing the spare onto the motor. Giant hassle .... some say removing the oil filter tower is not necessary however it is clear you need an inch of rearward mobility to disengage the ip from its studs, the rack bolt is too close to the filter tower as is the vacuum shut off actuator.

Any comment about that....

thanks for your comments....

No you do want the thinner in the fuel handeling portion of the injection pump. Plus you want to do this with the injection pump still on the engine.

If anything is gummed or sludged up it will be in the fuel circuit portion of the pump probably.

By doing it on the car you can check results and also may eliminate a pump change. Small chance of success but also small amount of effort at the same time.

My best hope is that someone tried to run that engine on waste vegatable oil at one time and there are perhaps lumps of fat interfering with something. The thinner will dissolve that type of thing quite well. I never trust injection pumps that have been sitting around off cars unless either full of fuel or submerged in a storage medium.

Load the laquer thinner by any method you wish. Pumping it in of course is the best as it will displace the diesel fuel by flowing it out the return. Do not rotate or start the engine with the laquer thinner in there.

Pump fresh diesel into the injection pump to flush the laquer thinner out of the pump before trying to start and run after the soak. On gas engines this is not a requirement as the thinner burns quite well as a gasoline substitute.

If this does not clear up the problem there are a couple of more things to try before changing out the pump.

I decided upon this approach a long time ago as a way to avoid rebuilding mercedes zenith carbs that had gummed up with dried gas residue. The altenative of knocking the two carbs down and kitting them was the other choice. .

My best hope is that someone tried to run that engine on waste vegatable oil at one time and there are perhaps lumps of fat interfering with something. The thinner will dissolve that type of thing quite well. I never trust injection pumps that have been sitting around off cars unless either full of fuel or submerged in a storage medium.

Yes you make a good point, it was sitting 1.5+years with fuel becoming stale,

care to mention briefly the other approaches so I can cogitate on them?

thanks again

One easy test to try is to back off the Vertical Throttle stop, (the idle speed screw between the block and IP), and the Rack Damper Bolt in the back of the IP, several turns and see if the engine returns to Idle faster. I am betting it will. Of course the Idle speed will be lower, (I will bet too low given your statement that it will not idle when cold), and the engine will idle ruffer, but both can be corrected with a different adjustment depending on the results of the test. This test is easy to do, and you can always just turn it back after the test if it did nothing.

If after backing out the Vertical Throttle Stop, and the Reack Damper, several turns, (at least 4, however depending on how far out of range it is it may not take that many to see an improvement), then there is something gummed up, (linkage, elements, return springs, etc).

The problem you are describing is common on 616 IPs due to how they are adjusted internally, (they also have an idle speed adjustment knob on the dash), and I have gone into a few of them and readjusted the Idle Governors so they operate correctly. I also have seen, and corrected, this problem on 616 and 617 IPs that people tried to turn up the torque control using instructions posted in various forums.

The above test will tell whether the Idle Governor is adjusted correctly or not. Like Barry said, changing the IP is a pain, can open up a can of worms, and there is no guarantee that it will be any better.

Well fixate on the attempted clean out first. Then I would read up and change the shutoff valve.

As long as the pump was full of diesel fuel it could sit a very long time. The fuel does not go stale like gasoline. But if there were some water in the pump with the fuel besides rust algea growth is possible. Remember some owners almost never change their filters. Water can accumulate in them over time as these cars do not have a water trap. At some point it will be fed forward to the injection pump. Almost all diesels in the developed and undeveloped world have water separators that are drainable. Just not mercedes for some reason. Even the humble volkswagon has two systems to cope with accumulated water and a warning light it is present.

Try to capture the output of the relief valve when clearing out the solvent. You want to see what comes out. In fact mention it.

barry, have you ever flushed lacquer thinner thru a diesel IP?

barry, have you ever flushed lacquer thinner through a diesel IP? If so with what result?